linux-kernel - Re: [PATCH 02/14] dt-bindings: soc: milbeaut: Add Milbeaut trampoline description

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Message-ID: <daa5f00a-1d9c-69b0-ed2d-8ff6a64251cc@socionext.com>
Date:   Tue, 22 Jan 2019 20:36:03 +0900
From:   "Sugaya, Taichi" <sugaya.taichi@...ionext.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Stephen Boyd <sboyd@...nel.org>, devicetree@...r.kernel.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Russell King <linux@...linux.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH 02/14] dt-bindings: soc: milbeaut: Add Milbeaut trampoline
 description

Hi

On 2018/12/04 22:32, Rob Herring wrote:
> On Tue, Dec 4, 2018 at 5:30 AM Sugaya, Taichi
> <sugaya.taichi@...ionext.com> wrote:
>>
>> Hi
>>
>> On 2018/12/04 0:49, Rob Herring wrote:
>>> On Mon, Dec 3, 2018 at 1:42 AM Sugaya, Taichi
>>> <sugaya.taichi@...ionext.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> On 2018/11/30 17:16, Stephen Boyd wrote:
>>>>> Quoting Sugaya, Taichi (2018-11-29 04:24:51)
>>>>>> On 2018/11/28 11:01, Stephen Boyd wrote:
>>>>>>> Quoting Sugaya Taichi (2018-11-18 17:01:07)
>>>>>>>>      create mode 100644 Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
>>>>>>>>
>>>>>>>> diff --git a/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt b/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
>>>>>>>> new file mode 100644
>>>>>>>> index 0000000..f5d906c
>>>>>>>> --- /dev/null
>>>>>>>> +++ b/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
>>>>>>>> @@ -0,0 +1,12 @@
>>>>>>>> +Socionext M10V SMP trampoline driver binding
>>>>>>>> +
>>>>>>>> +This is a driver to wait for sub-cores while boot process.
>>>>>>>> +
>>>>>>>> +- compatible: should be "socionext,smp-trampoline"
>>>>>>>> +- reg: should be <0x4C000100 0x100>
>>>>>>>> +
>>>>>>>> +EXAMPLE
>>>>>>>> +       trampoline: trampoline@...C000100 {
>>>>>>> Drop the 0x part of unit addresses.
>>>>>>
>>>>>> Okay.
>>>>>>
>>>>>>
>>>>>>>> +               compatible = "socionext,smp-trampoline";
>>>>>>>> +               reg = <0x4C000100 0x100>;
>>>>>>> Looks like a software construct, which we wouldn't want to put into DT
>>>>>>> this way. DT doesn't describe drivers.
>>>>>> We would like to use this node only getting the address of the
>>>>>> trampoline area
>>>>>> in which sub-cores wait.  (They have finished to go to this area in previous
>>>>>> bootloader process.)
>>>>>
>>>>> Is this area part of memory, or a special SRAM? If it's part of memory,
>>>>> I would expect this node to be under the reserved-memory node and
>>>>> pointed to by some other node that uses this region. Could even be the
>>>>> CPU nodes.
>>>>
>>>> Yes, 0x4C000100 is a part of memory under the reserved-memory node. So
>>>> we would like to use the SRAM ( allocated 0x00000000 ) area instead.
>>>> BTW, sorry, the trampoline address of this example is simply wrong.  We
>>>> were going to use a part of the SRAM from the beginning.
>>>>
>>>>>
>>>>>>
>>>>>> So should we embed the constant value in source codes instead of getting
>>>>>> from
>>>>>> DT because the address is constant at the moment? Or is there other
>>>>>> approach?
>>>>>>
>>>>>
>>>>> If it's constant then that also works. Why does it need to come from DT
>>>>> at all then?
>>>>
>>>> We think it is not good to embed constant value in driver codes and do
>>>> not have another way...
>>>> Are there better ways?
>>>
>>> If this is just memory, can you use the standard spin-table binding in
>>> the DT spec? There are some requirements like 64-bit values even on
>>> 32-bit machines (though this gets violated).
>>
>> The spin-table seems to be used on only 64-bit arch. Have it ever worked
>> on 32-bit machine?
> 
> Yes.
> 
>> And I would like not to use it because avoid violation.
> 
> The issue now that I remember is cpu-release-addr is defined to always
> be a 64-bit value while some platforms made it a 32-bit value.
> 'cpu-release-addr' is also used for some other enable-methods.

I have a question about the spin-table.
The code "smp_spin_table.c" is only in "arch/arm64/kernel" directory so 
can not be compiled in arm-v7 arch. That means the spin-table can not be 
used arm-v7 arch..? , or is there the way to compile the code in arm-v7 
arch?

Thanks,
Sugaya Taichi

> 
> Rob
>